On Thursday, the 17-year-old senior flies to Washington, D.C., where top scientists from around the country will grill him and 39 other semifinalists in the last round of the prestigious Westinghouse Science Talent Search.

The 10 students who make the final cut, to be announced Monday night, will win scholarships of $10,000 to $40,000. Only one other semifinalist is from Illinois, Irwin Lee of Naperville North High School.

``I`m not even going to try to calm down,`` said Joe. ``It`s just not possible.``

So why worry, just because scientists from Harvard, Princeton and Yale will test the competitors` mental mettle in two days of grueling interviews?

``They ask them all kinds of off-the-wall questions to find out about their deep-down creativity,`` says Horton, who sports a lapel button reading

``Physics

Fun.``

But some days are not so fun. Joe types furiously, communicating on-line with staff at Cornell University who help run the supercomputer he used for complex equations in his Westinghouse project on heat conduction.

His research shows how common laboratory techniques measuring the speed of heat traveling through solids are affected by outside variables like physical supports touching the solid. The supercomputer, accessed by telephone, allowed Joe to run programs in one hour that would take other computers four days. But people aren`t always as swift. Joe has not been able to obtain a video of his computer simulations in time. Instead, he`ll have to settle for still color photographs.

That`s just one small glitch after months of late-night research, aided only by a computer, soda pop and junk food. ``I don`t relax,`` said Joe, who hopes to study mechanical engineering at Stanford University next year. ``It`s hard to relax.``

Relaxing is definitely not the plan for the 167 students like Joe who spend three years at Evanston High in a rigorous honors science program that produces Westinghouse finalists and Ivy Leaguers each year, Horton said. With two periods of chemistry or physics each day for three years, the ``Chem-Phys`` program encourages students to work in teams and study groups.

Last year, a team of four students, including Joe, won a national contest that awarded access, training and equipment to use the Cornell supercomputer. Students at the Illinois Mathematics and Science Academy in Aurora also were winners.

Many of the students say they enjoy the hard work and long study hours in a program that challenges them.

``They`re trying to drill in a way of thinking,`` said Geoffrey Phillippe, a senior. ``You think problems down to all the little parts.``

The group atmosphere encourages students to support each other.

``Learning from each other is really, really important in this program,`` said Doran Fink, 16, a junior. ``Kids who aren`t doing as well as they want can get help from the hot shots.``

The help isn`t always scientific. When a sophomore student did badly in a math team competition, some kids on the team made him feel pretty bad. Sarah Hayford, who is ranked first in the junior class, circulated a card of apology that everyone signed and sent to the previously chastised youth, Horton said. ``This is really a group thing,`` Sarah said. ``And it`s nice to know there are other people as stressed out as I am.``